Cardinal numbers are used to count a quantity or to answer the question 'how many?'. In the given information, '25' represents the total number of participants, indicating 'how many' participants there were. Therefore, 25 is a cardinal number.

Ordinal numbers are used to indicate position, rank, or order. 'third' indicates the specific position of the question Sunil answered, and '7th' indicates Sunil's finishing position in the competition. Both 'third' and '7th' tell us 'which one' in a sequence. Therefore, 'third' and '7th' are ordinal numbers.

Based on this, the correct identification is: Cardinal: 25; Ordinal: third, 7th.

Option A is incorrect because '7th' is an ordinal number, not a cardinal number. Option C is incorrect because '25' is a cardinal number, not an ordinal number, and 'third' and '7th' are ordinal numbers, not cardinal numbers. Option D is incorrect because 'third' is an ordinal number, not a cardinal number, and '25' is a cardinal number, not an ordinal number.